1. Field of the Invention
This invention is directed to metal/gas batteries and fuel cells employing gas electrodes, and, more particularly, to a process for removing residues from fabricated gas electrodes prior to assembly of the battery or fuel cell.
2. Description of the Prior Art
A metal/gas battery or fuel cell comprising a gas electrode comprises a plurality of positive electrodes, a plurality of negative electrodes and an electrolyte. Expanded mesh screen, woven wire mesh and punched metal foil have variously been used in the prior art as electrode substrates. Patent applications Ser. Nos. 066,987 (now U.S. Pat. No. 4,250,235, issued Feb. 10, 1981) and 066,989 now U.S. Pat. No. 4,283,884 provide a novel etched nickel foil electrode substrate for nickel/hydrogen batteries which results in (a) lower electrical losses as compared with the same weight electrodes of other constructions and (b) more efficient packing density in the pressure vessel containing the electrodes. The etched foil electrode substrates are used for both positive and negative electrodes and are conveniently electrochemically etched from nickel sheet material in a grid mesh pattern.
In the fabrication of gas electrodes, porous polytetrafluoroethylene film (available from W. L. Gore & Assoc., Inc., Elkton, Md., under the trademark GORE-TEX) is attached to one side of the electrode substrate. The opposite side of the electrode substrate is provided with an electrochemically active coating comprising a mixture of platinum powder and small polytetrafluoroethylene particles. This coating is conveniently applied by silk screening a paste of fuel cell grade platinum black mixed with polytetrafluoroethylene particles held in suspension with TRITON X-100 non-ionic surfactant (available from Rohm and Haas Company, Philadelphia, PA). The negative electrode assembly is then sintered by slow heating over a one hour period to about 320.degree. C. and held at that temperature for ten minutes. The fabricated electrodes are then allowed to slow cool.
Heating to about 320.degree. C. is done, inter alia, to decompose and remove residues of the suspending agent. However, it has been found that residues of the suspending agent still remain, consequently providing conditions conducive to "flooding" and concomitantly reduced current density, along with a higher polarization than desired.